A Study On Selective Laser Melting Of Zr-Fe-Cu-Al Bulk Metallic Glass

Zr-based metallic glasses are alloys with short-range ordered structure and long-range disordered structure.Because of its unique atomic structure and excellent properties,Zr-based bulk metallic glasses have attracted great interest from researchers.However,even though the copper suction casting method in the preparation of bulk metallic glasses has the high cooling rate,there are still critical size limit,and due to the properties of the metallic glasses are hard brittle,it is not easy to process them into complex geometry,the above two problems have severely restricted the metallic glasses in the field of practical engineering application.Selective laser melting technology has the characteristics of high cooling rate and small molten pool stacking forming,which is expected to break through the problems of size limitation and difficult deformation existing in the traditional method of preparing bulk metallic glasses.In order to promote the application of bulk metallic glasses in practical engineering field,a new approach is developed and created.In this paper,for the additive manufacturing of Zr-Fe-Cu-Al system metallic glasses,first thing is to solve the general problems that bulk metallic glasses have which are glass forming ability and thermal stability,in the original metallic glasses system,the method of machine learning is used to optimize the alloy composition,and the method of experiment is used to verify the calculation results.Then,the crystallization behaviors of metallic glasses at low/high heating rates were studied to explore the feasibility of selective laser melting for the preparation of bulk metallic glasses.The causes of defects in the process of selective laser melting are studied.The large-sized Zr60Fe10Cu20Al10 bulk metallic glass was prepared by selective laser melting,and the mechanical properties and corrosion resistance of the samples were tested.The main results are as follows:Through random forests and the method of BP neural network,two classifiers are established according to the problems of:1.whether can the alloys form the amorphous state?2.How is the glass forming ability of the alloys that can form amorphous state?Several new compositions were found,then two of them were chosen(Zr64Fe1.5Cu24.5Al10,Zr63Fe2.5Cu23Al11.5)for applying the experimental verification,by casting method,the two alloys of Zr-Fe-Cu-Al alloy in different diameter were made,the obtained alloy bars were analyzed by XRD,DSC,etc.,and the calculated Zr64Fe1.5Cu24.5Al10 and Zr63Fe2.5Cu23Al11.5 components were confirmed to have stronger glass forming ability,which is of great help to the preparation of samples with high amorphous content during the additive manufacturing process.In order to study the crystallization of metallic glasses under different heating rate,the Zr60Fe10Cu20Al10 and Zr63Fe2.5cu23al11.5 crystallization process of metallic glasses were studied by DSC,the study found that in the crystallization process of system of Zr-Fe-Cu-Al metallic glasses,the nucleation dominated most of the crystallization,at the same time using in situ transmission electron microscopy in the process of heating Zr60Fe10Cu20Al10 had been used to characterize the crystallization process of metallic glasses.The experimental results are consistent with the crystallization process derived from theoretical calculation.The interaction between casting Zr60Fe10Cu20Al10 metallic glasses and laser is studied,first of all,in the different laser exposure time and laser power parameters,crystal grain size and crystal phase distribution were analyzed,and then adopt the method of finite element simulation for the interpretation of the above experiments.It is found that with the extension of laser exposure time or the increasing of laser power,the crystal phase content of metallic glasses increases,and the crystal phase is generated mainly in the heat-affected zone of laser action.By using the method of single layer spread powder,prepared single line samples under different process conditions to find the process window of reduce balling,the study found that balling phenomenon mainly comes from the molten-drop in the process of sample preparation is not fully spread,through calculating the composition of molten-drops completely spread out time to guide the process optimization;The hole defects of bulk samples were characterized,the effects of different process parameters on the hole were explained,and the method of process parameters adjustment to reduce the hole was defined.According to the morphology of the crack,the reason of generation of the cracks is explained,and by explaining that the temperature gradient is the main source of residual stress in this study,a method to suppress the crack is put forward by reducing the temperature gradient.Large-size Zr60Fe10Cu20Al10 bulk metallic glasses were prepared by selective laser melting.By means of groping of laser process parameters,the process parameters needed for preparation of the large-size bulk metallic glasses were found,and by optimizing the process parameters to find the method of eliminating defects such as cracks and holes in the sample,and by adjusting the process parameters on crystal phase content and regulation in order to achieve the required performance.By testing the mechanical properties and corrosion resistance of the selected laser melting samples,we can be sure that the large-size Zr60Fe10Cu20Al10 bulk metallic glasses obtained by the selected laser melting has better deformation ability than the casting sample on the premise of maintaining good corrosion resistance.